flyingbunny wrote:

I took the free test of GMAT club. One of the questions is as below.

I choose that "the last digit is 3", but the answer key says "the last digit is 7". The answer key is incorrect, isn't it?

well that reduces into 3^27 right? now you should know the pattern of 3^p is:

1,3,9,7,1,3 etc. starting from p=0. so 28/4 7. So you get to 7. 28 is 27 (1-27) + 1(0th power). It is also simple to count if you really wanted.

Just to clarify - since the pattern for 3^p happens every 4 powers when you divide the power by 4 the remainder determines the position of the digit. In this example .25 = 1, .5=3,.75=9, 1 (or nor remainder) = 7.

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